An Overlay Transport Virtualization (OTV) protocol has been developed to connect a Layer-2 network domain that spans across multiple data centers. The OTV protocol uses a “MAC-in-Internet Protocol (IP)” encapsulation technique to provide Layer-2 Virtual Private Network (VPN) solutions and extend the Layer-2 domain over an IP network. Since the OTV protocol uses IP, it does not require any pseudo-wire or tunnel maintenance and provides a multi-point connectivity using any available transport.
In a multi-homed topology where IP connectivity can be by more than one edge device at a site, the OTV protocol supports only a per-virtual local area network (VLAN) load-balancing. For a given VLAN, only one of the OTV edge switches forwards the packet in and out of the network. This works well for a typical Spanning Tree Protocol (STP) deployment, since the STP always blocks one of the redundant paths in a VLAN. However, in topologies that use Virtual Port Channel (vPC) and Data Center Ethernet (DCE), each of which supports multiple paths to reach a destination and per-flow load-balancing, active-active multi-homing support for OTV within a VLAN is needed.